Archive: Oct 2022

Accommodating Bore Configurations for Your Shaft Collar or Coupling

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Stafford Manufacturing Corp. designs and manufactures rigid couplings, shaft collars, and specialty mechanical parts used in automation, power transmission, motion control, and other OEM and MRO applications. We have collars and couplings available in square, threaded, hexagonal, keyed, and round bore configurations. In addition, we can add drive slots, press-fits, pulleys, or other special parts to meet your needs.

Here you’ll learn about each of these bore options and how to decide on the ideal shaft collar or coupling for your application. 


Types of Collar and Coupling Bore Configurations

Shaft collars and rigid couplings are machine components that slide over a shaft and lock into place with either set-screws or with clamping screws. They have three primary functions:

  • Holding components in place
  • Creating a connection between a shaft and another component
  • Positioning or locating parts along a shaft

Manufacturers supply variations of collars and couplings in different sizes, designs, and materials to fit a wide range of applications. Some of the common  shaft collar bore configurations include:

  • Round 
  • Threaded
  • Square
  • Hex
  • Keyed


Round Bores

As one of the most popular bore configurations, round shaft collars and couplings are used in various power transmission, motion control, and mounting applications. Serving as locators, spacers, bearing faces, or stops, they are most often used on shafts, tubing, pipes, and split hubs.

Round bore configurations are found in the following products:

  • One-piece shaft collars
  • Two-piece shaft collars
  • Hinge shaft collars
  • Threaded shaft collars
  • Heavy-duty shaft collars

Browse Stafford Manufacturing’s full selection of round bore shaft collars in our catalog

Browse Stafford Manufacturing’s full selection of round bore rigid couplings in our catalog

Round Bore Threaded Coupling
Round Bore Shaft Collar


Threaded Bores

Threaded shaft collars have a threaded interior that matches with certain threaded shafts. These provide superior grip, suitable for uses that require precise preload and location settings. Threaded shaft collars act as a stop to position parts or prevent them from moving along the shaft. 

Threaded bore configurations are found in the following products:

  • One-piece or two-piece split clamp UNF/ UNC Threaded Bore Shaft Collars
  • One-piece or two-piece Accu-Clamp™ Threaded Shaft Collars
  • One-piece or two-piece ACME Threaded Collars
  • One-piece or two-piece UNF/UNC Threaded Split Hub Collars
  • Threaded Hinge collars

See the threaded shaft collars we provide

Threaded Shaft Collar
Threaded Hinge Shaft Collar


Square and Hex Bores

Stafford Manufacturing produces hexagonal and square shaft collars and couplings to fit onto hexagonal and square-shaped shafts. Square and hex shaft couplings and collars are easy to install and customize with mounting capabilities if necessary. They provide high clamping power and are primarily used in food processing and conveyor systems. 

Square bore configurations are available in:

  • Two-piece split clamp styles collars
  • Mounting two-piece stackable styles collars
  • Precision Sleeve Rigid Couplings

Hex bore configurations are available in:

  • One-piece split clamp styles
  • Two-piece split clamp styles.
  • Precision Sleeve Rigid Couplings

Look through our full selection of hex and square shaft collars and couplings here.

Hex Bore Precision Rigid Coupling
Hex Bore Shaft Collar
Square Bore Precision Rigid Coupling
Square Bore Shaft Collar



Shaft couplings can be configured with keyways, but they are not always required. They should be utilized for couplings designed to support radial alignment and loads with high torque. Determine whether radial alignment or additional torque will affect the system’s overall operation, and then use that analysis to decide whether you need a keyway.

Keyed Rigid Coupling
Keyed Shaft Collar


Selecting Your Shaft Collar or Coupling Configuration

The right shaft collar or coupling is the one that fits your configuration and application.  In some cases, a certain type of configuration may be better than other options (i.e.  square, hex, and keyed shafts can handle more torque). Keyed shafts in particular have a locking position that makes accommodating higher torques possible.

Standard bores are cost-effective options that fit most basic applications. Stafford Manufacturing carries round, threaded, square, hex, and keyed bores as standard products, so our customers can rely on us to have what they need, when they need it. In addition, Stafford is the only stocking manufacturer of a full line of square and hex bore products.

While standard bore products serve most applications at the lowest cost, some applications require customized collars or coupling bores. Stafford has been manufacturing custom shaft collars and couplings for over 47 years and we can produce to your exact needs at a fair price with no minimum order quantity.

Stafford Is Your Custom Shaft Collar and Coupling Manufacturer

Stafford Manufacturing has nearly 50 years of industry experience. As an ISO 9001:2015-certified business, our staff has the quality control standards in place to produce the highest quality shaft collars and rigid couplings. We have a large selection of products, which enables us to assist you in selecting the ideal bore configuration for your particular needs and price range. If you can’t find a shaft collar or coupling that meets your needs, we will collaborate closely with you to design and produce a custom solution.

Contact us or request a quote today to learn more about our standard and custom offerings. 


How to Connect Shafts

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 Shaft couplings play a key role in transferring power or torque for motors, pumps, compressors, conveyors, turbines, and other mechanical equipment. Rigid shaft couplings can achieve this goal and allow for different types of shaft connections. Stepped couplings can be used for connecting different size shafts.  Shaft adapters can solve compatibility issues, such as changes in shaft size or length. Inch-to-metric couplings can solve incompatibilities occurring when mating an English shaft to a metric one.  Custom shaft couplings and adapters can accommodate unusual variations or configurations not satisfied by standard products.

Stafford Manufacturing produces shaft collars, rigid shaft couplings, and specialty mechanical products for motion control, power transmission, automation, and other MRO and OEM applications. Here we’ll discuss how to connect shafts, including those with different sizes, measurement systems, and other specifications.


Two-Piece Split Clamp-Style Coupling

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What If I Have Two Different Sized Shafts?

Connecting shafts of different sizes is a common issue that can be solved with compatible rigid shaft couplings. Designed for perfectly aligned shafts, rigid shaft couplings mate shafts with identical or different diameters while maintaining high torque transfer and preventing backlash. Many configurations of our shaft couplings have stepped bores to connect shafts that differ in size. We offer standard and custom versions of these types of rigid shaft couplings:


Two-Piece Split Precision Sleeve Coupling with Keyways

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 What If Need a Close Tolerance Fit?

A close tolerance fit is a necessity whenever you are putting the coupling on a precision machined shaft. Precision sleeve couplings are uniquely suited for applications requiring extremely precise machined shaft alignment and a close tolerance shaft-to-coupling fit.


Stafford’s exclusive Precision Sleeve Coupling features a solid center section that provides a close tolerance fit on ground shafting, includes a keyway, and the Accu-Clamp™ design which incorporates integral self-centering clamping collars at both ends. This product assures shaft alignment with zero backlash. To assure precise shaft alignment, it maintains <.001″ TIR concentricity while in use. It is precision machined, non-marring, easy to adjust, with high clamping power.

Stafford offers the following types of Precision Sleeve Couplings:


Inch-Metric Conversion Coupling

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What If I’m Connecting an Inch Shaft to a Metric Shaft?

Inch-metric conversion couplings have a bore on one side measured in inches and the other side in a metric size. Stafford Manufacturing carries a full range of common sizes in our selection of inch-metric conversion couplings. External dimensions and screws are in inches. These couplings can be further modified to include keyways if needed.

Our inch-metric conversion couplings can mate inch and metric shafts with zero backlash and smooth bores, which protect the shafts from damage. They have superior torque capacity compared to set screw type couplings.

Stafford offers the following types of inch-metric conversion couplings:


Step-Up Shaft Adapter

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What If I Need a Shaft Adapter?

While shaft couplings can connect shafts of different diameters, shaft adapters enable connections when:

  • One or both shafts are not long enough to be effectively connected with a coupling
  • Shafts differ in diameter and a coupling does not accommodate the difference
  • Shaft damage would result in a poor transfer of power or motion
  • Shaft replacement is not recommended due to cost or other considerations

Available in step-up or step-down configurations, shaft adapters act as both an extension to an existing shaft and as a way to increase or decrease shaft diameter using a straight-bore or standard stepped-bore coupling. Our rigid shaft adapters use a clamp-style attachment to avoid shaft damage and come in keyed and keyless styles. 


Rigid Shaft Coupling Configurator

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None of These Work for Me — What Do I Do?

Uncommon sizes or combinations of shaft diameters, shapes, keyways, or other configurations can be solved with custom shaft couplings or adapters, avoiding the need for complete shaft replacement or system reconfiguration. Customers can custom-design couplings through our rigid shaft coupling configurator tool, which can provide product recommendations based on your specifications.

Because manufacturing custom parts is our specialty, our expert team welcomes requests for customized rigid couplings to meet your precise requirements. Custom modifications we commonly make include:

  • Bores: adjustments for special diameters, keyways, and threadings
  • Outside Diameters: surface modifications (e.g. knurling, flats, pulley grooves, notches)
  • Holding Power: adjustments for extra heavy-duty operation
  • Circumferential Keyways: to control axial shift
  • Shaft Shapes: to connect different shaped shafts
  • Balancing: to minimize misalignment, vibration, and wear
  • Materials & Finishes: meeting customer material or surface finishing requirements
  • Shaft Extenders: to accommodate length, duty, configuration, or other needs

Customers may also modify our fully machinable Shaft Adapter Max to meet their specific needs. It is available with keyways or without, offering multiple configurations to easily extend and adapt for hex, square, or threaded shafts.

Custom Fabrication by Stafford Manufacturing

At Stafford Manufacturing, we pride ourselves on our wide range of standard shaft couplings, collars, adapters, and related products. Our innovative designs, extensive catalog of stock components, and customization capabilities illustrate our commitment to industry-leading components and customer service. Contact us to learn more about our standard and custom components for power transmission, motion control, automation, and related applications, or request a quote for your next project.



Stafford Manufacturing Corp.

256 Andover St.

Wilmington, MA 01887

Phone: 978.657.8000